Mac: Fix a recently introduced layering bug.

The code made assumptions about whether the window's root view was layer
backed. The CL that introduced the bug:
https://codereview.chromium.org/390503003/

BUG=NONE

Review URL: https://codereview.chromium.org/481273002

Cr-Commit-Position: refs/heads/master@{#291188}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@291188 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/cocoa/browser_window_controller.h

@@ -168,6 +168,9 @@ class Command;
   // The Extension Command Registry used to determine which keyboard events to
   // handle.
   scoped_ptr<ExtensionKeybindingRegistryCocoa> extension_keybinding_registry_;
+
+  // Whether the root view of the window is layer backed.
+  BOOL windowViewWantsLayer_;
 }
 
 // A convenience class method which gets the |BrowserWindowController| for a

chrome/browser/ui/cocoa/browser_window_controller_private.mm

@@ -683,6 +683,7 @@ willPositionSheet:(NSWindow*)sheet
       // Leaving wantsLayer on for the duration of presentation mode causes
       // performance issues when the dropdown is animated in/out.  It also does
       // not seem to be required for the exit animation.
+      windowViewWantsLayer_ = [[[self window] cr_windowView] wantsLayer];
       [[[self window] cr_windowView] setWantsLayer:YES];
     }
     NSView* contentView = [[self window] contentView];
@@ -920,7 +921,7 @@ willPositionSheet:(NSWindow*)sheet
 
   [self showFullscreenExitBubbleIfNecessary];
   browser_->WindowFullscreenStateChanged();
-  [[[self window] cr_windowView] setWantsLayer:NO];
+  [[[self window] cr_windowView] setWantsLayer:windowViewWantsLayer_];
   [self updateRoundedBottomCorners];
 }